This project is an investigation into the role of the medial lobe of the primate brain in memory. Three experimental paradigms will be used in a multidisciplinary approach to this subject. There are: behavioral testing of monkeys with selective brain lesions, electrophysiological recording of single unit activity, and anatomical investigation of the medial temporal lobe. The project centers around five main aims. 1) A computerized version of the Wisconsin General Test Apparatus will be developed to assess the effect of lesions to the hippocampus and overlying cortex on performance of a number of memory tasks. The new apparatus will allow precise measurement of hand and eye position to be made, leading to an understanding of the difficulties faced by lesioned animals at a much more precise level than has been in previous studies. 2) New techniques of analysis of neuronal responses will be developed in order to understand the computations performed at the neuronal level. These include methods of looking at temporal patterning in individual spiketrains, and methods of understanding neuronal responses at the level of the whole population of neurons. 3) The activity of single neurons in the hippocampus will be recorded in awake, behaving monkeys sets of tasks which test memory, discriminative etc., including those shown to be performed poorly after lesions of this region. 4) Neuronal activity will be related to visuospatial and motor-spatial aspects of tasks, in order to understand the relation of the hippocampus to the representation of space, and to understand the relation of spatial deficits and deficits in other tasks. 5) Anatomical investigations will proceed to outline the relation of different types of neurons, defined in terms of responsiveness, to different anatomical subareas. Tracer substances such as horseradish peroxidase, nuclear yellow and true blue will be injected into subregions which have been identified physiologically in that particular animal, in order to trace the interconnections of subregions related to certain aspects of task performance. By bringing together a number of different techniques, this study will attempt to explicate anatomical ("hardware") and neuronal ("software") constraints on the actual processing of information performed by the brain.